Influence of small amount of Al and Cu on the microstructure, microhardness and tensile properties of Sn-9Zn binary eutectic solder alloy

In the present study, a separate addition of the same amount of Al and Cu are added with the Sn-9Zn eutectic solder alloy to investigate the effect of a third element addition on the microstructural and mechanical properties as well as thermal behavior of the newly developed ternary solder alloys. The results indicate that both Al and Cu refine the microstructure and form intermetallic compounds with the eutectic solder alloy. The microstructures of the newly developed ternary Sn-9Zn-X solder alloys were composed of fine needle-like α-Zn phase with some IMC dispersed in the β-Sn matrix. The relatively small and compact shaped Al6Zn3Sn IMC was found to be uniformly distributed in the β-Sn phase which results in an increase in the tensile strength, due to the second phase dispersed strengthening mechanism. On the contrary, the large flower shaped Cu6Sn5 and rod shaped Cu5Zn8 IMC develops some sort of weak interface with the parent β-Sn matrix results in a decrease in the tensile strength. The microhardness of the Sn-9Zn-0.5Al ternary solder alloys was also higher than that of the Sn-9Zn-0.5Cu alloy.